Pointer to 2d array in c

I have written a lot of articles on array and pointer if you want you can see this link, C Tutorial. Nowadays many students ask me a question that how to access a multidimensional array with a pointer in C or access two dimensional array using pointers in C I have replied many students but every month I found this question in my Inbox. So I have decided to write an article on how to access a multidimensional array with a pointer Access two-dimensional array using pointers in C. In C-language pointer and array are very close to each other, an array can be split in the form of the pointer.

The name of the array is a pointer to its first element. So if acData is an array of character then acData will be the address of its first element. Note Array elements stored in a consecutive memory block, so we can access the elements of the array using the pointer.

In C language, the compiler calculates offset to access the element of the array. The calculation of the offset depends on the array dimensions.

Pointers and multidimensional arrays

Suppose int aiData[3][3] is a 2D array that has 3 rows and 3 columns. Now to access the element just add the offset in array base address and dereference it. We know that the array element is stored in the contiguous form so we can also access the elements of the two-dimensional array to calculate the total number of cells.

We can easily access a 2D array with the help of a pointer to the array. First, we need to define a new type for the 2d array using the typedef that helps you to avoid the complex syntax.

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After the creation of a new type for the 2d array, create a pointer to the 2d array and assign the address of the 2d array to the pointer. Similar to the two-dimensional array we can access three, fourth, … etc dimensional array using the pointers. Skip to content. About Amlendra I am an embedded c software engineer and a corporate trainer, currently, I am working as senior software engineer in a largest Software consulting company.

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Pingback: Pointer to string array in C - AticleWorld.Arrays in C or in any other programming language are container types that contain a finite number of homogeneous elements. Elements of an array are stored sequentially in memory and are accessed by their indices. Arrays in C language are static type and thence the size of array cannot be altered at runtime, but modern languages like Java, implement arrays as objects and give programmers facility to resize them at runtime.

Arrays become useful storage containers when the size of the list is know beforehand. Array name in C language behaves like a constant pointer and represents the base address of the array. It points to the first element of the array which is located at 0 th index. As array name serves like a constant pointer, it cannot be changed during the course of program execution.

To demonstrate how arrays in C are defined, and accessed by the item index? How they are accessed by the help of pointers? Let's go through the following program and the description. Array arr defined in above program contains 5 integer values stored at indices from 0 to 4. Array index starts from zero that's why index of the last element will be size of array minus one, that is, arr[4] in this case.

Below is the pictorial representation of arrwhere the array arr points to first element at location 0. This element has address that is the base address of the array and represented by the array name. Elements stored in an array are accessed by following the syntax "arrayName[index]" e. This strategy computes the base address of the desired element by combining the base address of the array with the index of desired element.

Every array element takes a fixed number of bytes, which is known at compile time and this is decided by the type of array. In above example array is of type integer thus consumes 4 bytes size of integer per element.

You can devise the following formula to compute n th element address. The square bracket [] syntax to access array elements deals with address computation at its own. It takes the index that you wish to access, multiplies it with the element size, adds this resulting offset to the base address of the array, and finally dereferences the resulting pointer to get the desired element. Now that you understand the computation of offset and then address of the element you want to access.

pointer to 2d array in c

Any element in the valid range of array can also be accessed by adding the index of that element to the base address and it computes the same offset as it was computed by square bracket syntax. But it leaves the result as a pointer and you have to dereference it at your own. The two expressions only differ by whether the pointer is dereferenced or not. In fact those two probably compile to exactly the same code. They both represent a pointer to the element at index 3.

We just need to add in the pointer dereference. Pay attention to the following lines to understand correct syntax of dereferencing.

Likewise, can you write arr[3] to 3[arr]? Yes, you can.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information.

I have an example involving a pointer to a 2D array. Can someone help me understand what is going on in this example? The for loop in your program is used to identify which row has the maximum value of the sum of its elements 3 elements.

Once the control comes out of that for loop, Ptr will be pointing to the row which has the maximum sum of its elements and sum0 will have the value of the sum.

Consider an array int a[5];I hope you know that a[0] and 0[a] is the same. This same logic can be used in 2 dimensional array.

We can write it as i[data][j] also. So, Ptr now points to the address of first column in first row. The second zero is the column no. So, first row and first column's memory address is chosen.

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Using pointer arithmetic is treating 2d array like 1D array. Adding a number higher than column number would simply continue counting the elements from first column of next row, if that exists. More precisely, data is an array of 3-element arrays of int, which behaves like a pointer to 3-element arrays of int; adding i to it moves past i such arrays. The usual way to access other columns of the array is ordinary array indexing. If you refer to data[i][j]you're getting column j of row i.

If you want to do it with explicit pointer arithmetic, then note that e. But, as a matter of style, you should generally not do explicit pointer arithmetic when you don't actually need to. In your example the loop goes through all matrix rows to find the one whose sum of all elements holds the maximum value. Notice that Ptr is a pointer so it holds a memory address, hence Ptr is different than 23 unless the memory address happens to be 23which is unlikely to happen. Learn more. Ask Question. Asked 7 years, 9 months ago.

Active 2 years, 6 months ago.

C - Pointers and Two Dimensional Array

Viewed 54k times. I was taking an intro CS course and this was just an example given from my lecture notes. Active Oldest Votes. For more details please refer to the book "understanding pointers in c" by yashwant kanetkar. Doing so, you are declaring pointer to an 2D array. Sanjeev Maharjan Sanjeev Maharjan 1 1 silver badge 6 6 bronze badges.When an array is declared, compiler allocates sufficient amount of memory to contain all the elements of the array. Base address i.

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Assuming that the base address of arr is and each integer requires two bytes, the five elements will be stored as follows:. Here variable arr will give the base address, which is a constant pointer pointing to the first element of the array, arr[0]. Hence arr contains the address of arr[0] i. In short, arr has two purpose - it is the name of the array and it acts as a pointer pointing towards the first element in the array. As studied above, we can use a pointer to point to an array, and then we can use that pointer to access the array elements.

Lets have an example. We can also use the Base address a in above case to act as a pointer and print all the values. A multidimensional array is of form, a[i][j]. Lets see how we can make a pointer point to such an array. As we know now, name of the array gives its base address.

How to access two dimensional array using pointers in C programming?

Pointer can also be used to create strings. Pointer variables of char type are treated as string. The above code creates a string and stores its address in the pointer variable str. The pointer str now points to the first character of the string "Hello".

Another important thing to note here is that the string created using char pointer can be assigned a value at runtime. Notice that str is pointer to the string, it is also name of the string. We can also have array of pointers. Pointers are very helpful in handling character array with rows of varying length. In the second approach memory wastage is more, hence it is prefered to use pointer in such cases.

When we say memory wastage, it doesn't means that the strings will start occupying less space, no, characters will take the same space, but when we define array of characters, a contiguos memory space is located equal to the maximum size of the array, which is a wastage, which can be avoided if we use pointers instead.

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Made with by Abhishek Ahlawat. Ruby Servlet JSP. Operating System. Computer Architecture. Jenkins Maven. Apache Cordova Drools. We are Hiring! Sign in.How to access two dimensional array using pointers in C programming? Write a C program to input and print elements of a two dimensional array using pointers and functions.

pointer to 2d array in c

Multi-dimensional arrayPointersPointers and ArraysFunctions. To access a two dimensional array using pointer, let us recall basics from one dimensional array. Since it is just an array of one dimensional array. Now we know two dimensional array is array of one dimensional array. Hence let us see how to access a two dimensional array through pointer.

I have tried to summarize two dimensional array access using pointer in below image. Two dimensional array access using pointer. The first int matrix[][COLS] is general array notation.

Example Input Input elements in 3x3 matrix: 1 2 3 4 5 6 7 8 9 Output Elements of 3x3 matrix: 1 2 3 4 5 6 7 8 9. Enter elements in 3x3 matrix. Recommended posts Array and matrix programming exercises index.

pointer to 2d array in c

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Have a doubtwrite here. I will help my best. Before commenting you must escape your source code before commenting.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information.

Rather than referring to int[2][3] as a '2d array', you should consider it to be an 'array of arrays'. It is an array with two items in it, where each item is itself an array with 3 ints in it. You can use p to point to either of the two items in a. To initialize p to point to the second element, use:. When you write. It declares p as a pointer to the first element which is an array.

How to access two dimensional array using pointers in C

So, p points to the array of 3 ints which is a element of array of arrays. Here, p is your pointer which points to the array of 3 ints which is an element of array of arrays.

It is a pointer to the first element of a. The first element of a is an array of three ints. The numeric value of p and q are likely or maybe even required to be the same, but they are of different types.

This will come into play when you perform arithmetic on p or q. The [3] is a part of the type. In this case p is a pointer to an array of size 3 which holds ints. Learn more. A pointer to 2d array Ask Question. Asked 8 years, 3 months ago.

pointer to 2d array in c

Active 1 year, 2 months ago. Viewed 56k times. I have a question about a pointer to 2d array. If an array is something like int a[2][3]; then, is this a pointer to array a? Active Oldest Votes. Gabriel Staples 5, 3 3 gold badges 34 34 silver badges 63 63 bronze badges. You could even write [3]a for example : It's a good way of learning what arrays in C really are.

Is this one pointer, or 65 pointers?

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Blagovest Buyukliev Blagovest Buyukliev Thanks for your comment. If this is the case, where is a room for [2]? Or does it points to [0][0] and [0][1]?

It doesn't know that the first dimension of a is 2, because it is assigned to the first element of awhich is exactly of type int[3]. MarianD 5, 6 6 gold badges 21 21 silver badges 35 35 bronze badges. The OP asks a conceptual question and I have answered it here. In place of 5 put 3!.

Also I have added more details on how to obtain value from 2d arrays using pointers. I would argue that this is more confusing than the rest of the answers provided here.C Programming. In this tutorial we will learn to work with two dimensional arrays using pointers in C programming language. In the previous tutorial Pointers and One Dimensional Array we learned to work with one dimensional character array. Feel free to checkout that tutorial.

To keep things simple we will create a two dimensional integer array num having 3 rows and 4 columns. The compiler will allocate the memory for the above two dimensional array row-wise meaning the first element of the second row will be placed after the last element of the first row. And if we assume that the first element of the array is at address and the size of type int is 2 bytes then the elements of the array will get the following allocated memory locations.

We have created the two dimensional integer array num so, our pointer will also be of type int. The two dimensional array num will be saved as a continuous block in the memory. So, if we increment the value of ptr by 1 we will move to the next block in the allocated memory.

In the following code we are printing the content of the num array using for loop and by incrementing the value of ptr. We can compute the address of an element of the array by using the rows and columns of the array. For this we use the following formula. Where, arr is a two dimensional array. Where, arr is a two dimensional array and i and j denotes the ith row and jth column of the array. In the following example we are finding the value at the location 2nd row and 3rd column of the array num.

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